Earth is a planet born of fire.
For billions of years, volcanoes have helped create the world we know. From the continents to the air we breathe and even life itself, all have their origins in fire. These processes have created extraordinary...

Grab your mask and snorkel and come on an unforgettable adventure! Great Barrier Reef captures the natural beauty of the world’s largest living wonder and introduces us to the visionaries and citizen scientists who are helping us better understand this...

Join an immersive IMAX adventure to experience the life-saving superpowers and extraordinary bravery of some of the world's most amazing dogs. No stranger to superheroes himself, Chris Evans narrates this inspiring true story about remarkable (or is that...

The Fleet's newest exhibition, Pause|Play, is an invitation for the young and the young-at-heart to leave the digital world behind, hit pause on their busy lives and recapture the nostalgia of play. Science has shown that play has a number of cognitive,...

As Tim Gunn is fond of saying, “Make. It. Work!” And that’s the idea behind our Make-It Workshop, a creative and interactive workshop for innovators and other curious minds. We invite you to stop by Studio X (formerly Tinkering Studio) on Saturdays to...

Stay and play—and save!—until 10 p.m. on Friday nights this summer!
Bring the entire family to experience the Fleet at night! Enjoy extended evening hours at the Fleet in celebration of The Art of Summer in Balboa Park. Peruse Pause|Play late into...

Grownups! You get the science center all to yourself (no kids allowed!) to explore exhibits at a savings, enjoy an adult beverage and rock out to music on Saturday nights this summer.
Adult Recess provides your chance to take over the Fleet's...

The first Monday of every month, seniors 65 and better can enjoy the Science Center exhibits, a show in the Heikoff Giant Dome Theater and a lecture on the quietest day of the month for only $10! No coupons or additional discounts are accepted. The Fleet...

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Join us on the first Wednesday of each month at 7 p.m. or 8:15 p.m. for a tour of the solar system narrated by the Fleet’s astronomer. Journey through the cosmos with us as we explore a new topic each month.
For optimal viewing, each show is...

Join us on the second weekend of each month to investigate exciting science topics. Sessions will be filled with new challenges, hands-on activities and interaction with local scientists. Throughout the year, we will explore an array of fields including...

Did Comets Deliver Water or Nitrogen to Earth?

By David Harker, Associate Research Scientist, UCSD Center for Astrophysics and Space Sciences (CASS)

In an earlier post, I pointed out that one of the primary science questions that the Rosetta mission is hoping to address during its rendezvous with comet 67P is whether the Earth's current day oceans were composed of water delivered by comets. It is theorized that during the heavy bombardment era, which occurred some 3.8 to 4.1 billion years ago, water was delivered to Earth via comets, much like comet 67P.

Based on the current analysis of the data from Rosetta, the answer appears to be no, comets such as 67P did not contribute significantly to the Earth's oceans. However, this finding does not end the debate over whether comets deposited materials onto the young Earth. In fact, it raises more questions.

First a quick reminder about what Rosetta is looking for when it comes to water in comet 67P. Water contains hydrogen which is composed of a single proton and a single electron. Water also contains a heavier isotope of hydrogen called deuterium which is composed of a proton and an electron just like hydrogen, but also an extra neutron.

For the most part, the ratio of deuterium to hydrogen in water (called the D/H ratio) is a fixed quantity once the water is formed. This can happen when the hydrogen and oxygen molecules bond here on Earth or when they bonded on comets in outer space many millennia ago. During the Earth's formation it is thought that all of the water on Earth boiled off, requiring the delivery of water from other solar system bodies, such as comets and asteroids. By comparing the D/H ratio of the Earth's oceans to the D/H ratio of the ice on comet 67P, scientists can better theorize whether the water on Earth was derived from water that bonded on comets such as 67P.

What Rosetta has found is the D/H ratio in 67P is three times higher than the D/H ratio of the water in the Earth's oceans. This makes it highly unlikely that comets such as 67P could have contributed to the Earth’s oceans.

All is not lost though! Another intriguing development is that Rosetta also discovered molecular nitrogen in comet 67P. This is the first time molecular nitrogen has been measured in a comet. Perhaps nitrogen was deposited on Earth by comets!

What Rosetta found is that there is too little molecular nitrogen in comet 67P compared to the Earth. So just as with the water, it seems like comets such as 67P were not significant contributors to Earth's nitrogen content either.

While it might seem like these two developments represent “non-discoveries,” remember that scientific discovery can come from ruling out other potential options just as readily as it can come from confirming a theory to be correct. Comets such as 67P may not have been the source of water or nitrogen on Earth, but that still leads to a world of amazing discoveries that can be made about comets, asteroids and the geological past of our own planet.